Difference-in-differnce with zero inflated data

[mag_newbie]

Hello everybody,

I did a differnce-in-difference anlysis for in health care expenditures using proc genmod and %NLEstimate. People participating in a stuctured health care programme (Prog=1) were compared to those who do not participate (Prog=0). With data for both groups availabe for 1 year before intervention (post=0) and 1 year after intervention (post=1). The same subjects are measured before and after. The code I used works for the primary outcome "total cost". But now I need to analyse subcategories of costs, additinally (for hospitalisation, drugs,...) and some of these subcategories are zero-inflated.

Is there any option how I can make a DiD anaysis using zero-inflated data?

Any help would be greatly appreciated.

Maggie

proc genmod data= cost;
class prog post / ref= first;
model total_cost= prog post prog*post / dist=gamma link=log;
estimate "diff_in_diff" prog*post  1 -1 -1 1;
lsmeans prog*post  / e linik;
lsestimate prog*post "diff_in_diff" 1 -1 -1 1;
store out= gammod;
run; 

data difdif;
input k1-k4;
set=1;
datalines; 
1 -1 -1 1;

%NLEstimate (instore= gammod,
label= Diff in Diff
f=(exp(b_p1+b_p2+b_p4+b_p6) - exp(b_p1-b_p4)) - 
(exp(b_p1+b_p2) - exp(b_p1)), 
title= DiD Totel cost)